The gradual accumulation of tritium in the heavy water of a CANDU (Canadian Deuterium Uranium) reactor is responsible for a substantial proportion of the radiological dose received by reactor operators. Tritium management is, therefore, becoming increasingly important as individual reactors require periodic detritiation.
For the scale of detritiation required to detritiate a CANDU reactor, cryogenic distillation of a mixture of hydrogen isotopes in the elemental form is the only applicable technology for concentration of the extracted tritium to near 100% purity. However, a tritium extraction plant (TEP) must first achieve a transfer of the tritium from the oxide form (DIO) to the elemental form (DT) for the distillation process.
Cryogenic distillation plants are expensive, with the cost of these plants scale insensitive to the volume of heavy water treated. Thus, there has been a need for a geographically centralized process to effect tritium extraction in order to reduce the need for individual tritium extraction and cryogenic distillation plants to be built for various reactors. The drawback of centralized tritium extraction, however, is shipping tritiated heavy water by conventional tanker and the public controversy that develops over the perceived threat of a spill. This perceived threat has resulted in severe restraints of the shipping of heavy water from the United States to Canada. Another drawback is that the cost effectiveness of centralized detritiation is affected by the quantity and value of heavy water that would be in transit at a given time between the centralized tritium extraction plant and the reactor site, especially as the distance between the TEP and the reactor site is increased.
The cost effectiveness of shipping tritiated heavy water is also affected by the degree of detritiation. A high level of detritiation is particularly desirable where deuterium has to be shipped over extensive distances and where the detritiated product has to be returned in water form.